A single virus, a vaccine strain of Venezuelan equine encephalitis virus, has been shown to act as an adjuvant or immunosuppressive agent for the antibody response; and to induce energy or significantly suppress the manifestation of delayed hypersensitivity. The objectives of the current studies are to determine the cell type, lymphocyte or macrophage, which is altered by the virus to prevent the expression of delayed hypersensitivity. The effect of virus infection on delayed hypersensitivity is being studied by the in vitro methods of macrophage migration and lymphocyte transformation with study of the mediators produced from lymphocyte transformation. The effect of VEE infection on in vitro responses to added dibutyryl cyclic AMP and theophylline is also being studied. Likewise, the cell type altered which influences the antibody response is under test. The conditions of antigen dose, route, form and time of immunization after VEE infection which leads to an adjuvant or suppressive effect on the antibody response are being determined.